condition of the rocks, the harder and tougher they are
the narrower as a rule being the valley.

From time to time a side stream enters the main valley. This is itself
composed of many smaller rivulets. If the lateral valleys are steep, the
streams bring with them, especially after rains, large quantities of
earth and stones. When, however, they reach the main valley, the
rapidity of the current being less, their power of transport also
diminishes, and they spread out the material which they carry down in a
depressed cone (Figs. 28, 29, 31, 32).

A side stream with its terminal cone, when seen from the opposite side
of the valley, presents the appearance shown in Figs. 28, 31, or, if we
are looking down the valley, as in Figs. 29, 32, the river being often
driven to one side of the main valley, as, for instance, is the case in
the Valais, near Sion, where the Rhone (Fig. 30) is driven out of its
course by, and forms a curve round, the cone brought down by the torrent
of the Borgne.

[Illustration: Fig. 29.--Diagram of an Alpine valley, showing a river
cone. Lateral view.]

Sometimes two lateral valleys (see Plate) come down nearly opposite one
another, so that the cones meet, as, for instance, some little way below
Vernayaz, and, indeed, in several other places in the Valais (Fig. 31).
Or more permanent lakes may be due to a ridge of rock running across the
valley, as, for instance, just below St. Maurice in the Valais.

[Illustration: Fig. 30.]

[Illustration: VIEW IN THE VALAIS BELOW ST. MAURICE. _To face page
266._]

[Illustration: Fig. 31.--View in the Rhone Valley, showing a lateral
cone.]

Almost all river valleys contain, or have contained, in their course one
or more lakes, and where a river falls into a lake a cone like those
just described is formed, and projects into the lake. Thus on the Lake
of Geneva, between Vevey and Villeneuve (see Fig. 33), there are several
such promontories, each marking the place where a stream falls into the
lake.

[Illustration: Fig. 32.--View in the Rhone Valley, showing the slope of
a river cone.]

The Rhone itself has not only filled up what was once the upper end of
the lake, but has built out a strip of land into the water.

[Illustration: Fig. 33.--Shore of the Lake of Geneva, near Vevey.]

That the lake formerly extended some distance up the Valais no one can
doubt who looks at the flat ground about Villeneuve. The Plate
opposite, from a photograph taken a